Modular Hybrid Transmission with a One Way Clutch

ABSTRACT

A vehicle transmission system having a combustion engine, an electric motor and a transmission includes a first clutch operatively connected between the engine and the motor and a one way clutch. The one way clutch is connected in parallel with the first clutch that permits the engine to increase speed with the clutch disengaged until the engine speed matches the motor speed. The engine provides positive torque through the one way clutch to the motor and transmission upon matching the motor speed. The first clutch and the one way clutch may be a hybrid rocker one way clutch.

TECHNICAL FIELD

This disclosure relates to a transmission for a vehicle that has acombustion engine that is connected by a one way clutch to an electricmotor and a transmission gear box.

BACKGROUND

Hybrid electric vehicles may connect a combination of an internalcombustion engine with an electric motor in series to provide the powerneeded to propel a vehicle for improved fuel economy over a conventionalvehicle. One way to improve the fuel economy of a hybrid vehicle is toshut down the engine during times that the engine operates inefficientlyand to use the electric motor to provide all of the power needed topropel the vehicle. The engine must start in a quick and smooth mannerthat is nearly transparent to the driver in the event the driver wantsmore power than the electric motor can provide or if the battery becomesdepleted.

A Modular Hybrid Transmission (MHT) is a pre-transmission parallelhybrid with a disconnect clutch positioned between the electric motorand the engine. The disconnect clutch is fully integrated into thetransmission hydraulic system and is actuated by a linear solenoid. MHThybrids represent one approach to providing a torque path for rear wheeldrive vehicles.

In a MHT system, the engine may be started independently of the motorthat is driving the vehicle. Once the engine is up to speed, thedisconnect clutch may be commanded to engage to allow the engine todeliver torque to the transmission. The motor speed may be below aminimum speed required to deliver robust line pressure before the enginestart request. If the line pressure is insufficient, application of thedisconnect clutch may become unpredictable.

Timing the application of the disconnect clutch is important with a MHTdesign. The clutch is a wet friction clutch that must be stroked beforetorque can be transmitted. The added flow volume for stroking the clutchwith the oil pump operating at low speed may cause an undesired drop inline pressure that may create a driveline disturbance. The drop in linepressure may have a deleterious effect on controlling the pressureapplied by the launch clutch or torque converter bypass clutch.

The above problems and other problems relating to modular hybrid systemsare addressed by this disclosure as summarized below.

SUMMARY

In the MHT design, the engine is never required to operate at a higherspeed than the motor. When the engine is off, the motor may operate at ahigher speed than the engine. A one way clutch (OWC) may be providedthat is connected between the engine and the motor in parallel with adisconnect clutch. The one way clutch prevents the engine fromover-running the motor. The one way clutch eliminates the need tosynchronously transfer torque from the motor to the engine as the engineincreases speed. This one way clutch simplifies the process of applyingthe clutch.

Alternatively, the friction clutch may be eliminated and a hybrid rockerone way clutch (HROWC) may be placed in series with the OWC. The HROWCis an electrically controlled device that is shifted between “applied”and “not applied” states. The rockers are open and torque is nottransmitted in either direction when the HROWC is not applied. When theHROWC is applied, the rockers are pulled in to allow slip in onedirection and full engagement in the other direction. The HROWC isapplied when the engine speed matches motor speed so that the engine islocked with the motor by the two OWCs. When the HROWC is not applied,the engine is allowed to operate at speeds less than the motor. Oneadvantage of this concept is lower spin losses of the open clutch duringelectric drive.

According to one aspect of this disclosure, a transmission system isprovided for a vehicle that has a combustion engine, an electric motorand a transmission connected in series. The transmission systemcomprises a disconnect clutch operatively connected between the engineand the motor, and a one way clutch connected in parallel with thedisconnect clutch that allows the engine to increase speed with thedisconnect clutch disengaged until it matches the motor speed. Aftermatching speeds, the engine provides positive torque to the motor andtransmission.

According to other aspects of the disclosure, the disconnect clutch maybe a wet clutch that is shifted by hydraulic pressure from a hydraulicpump. The one way clutch connects the engine to the transmission totransmit torque to a driveline of the vehicle when the engine speedmatches the motor speed. The speed of rotation of the engine is limitedby the OWC to the motor speed. The one way clutch may be a hybrid oneway clutch that has rockers that may be shifted to engage the clutch inone rotational direction.

According to another aspect of the disclosure, a transmission system isdisclosed for a vehicle that has a combustion engine, an electric motorand a transmission connected in series. The transmission systemcomprises a one way clutch that slips in a first rotational drivedirection, and a hybrid one way clutch having selectively shiftedrockers. The hybrid clutch is connected in parallel to the one wayclutch between the engine and the motor. The rockers are actuated whenthe engine speed matches the motor speed to shift the rockers from abidirectional slip condition to a one way slip condition locked in thefirst rotational drive direction.

According to further aspects of the disclosure, the rockers whenactuated may cause the hybrid clutch to slip in a second rotationaldrive direction. The one way clutch connects the engine to thetransmission to transmit torque to a driveline of the vehicle when theengine speed matches the motor speed.

According to another aspect of the disclosure as it relates to a methodof operating a transmission system for a vehicle that has a combustionengine, an electric motor and a transmission connected in series. Thetransmission system further includes a first clutch operativelyconnected between the engine and the motor and a one way clutchconnected in parallel with the first clutch. The method includes thesteps of initiating an engine start operation, disengaging the firstclutch to disconnect the engine from the electric motor, and engagingthe one way clutch when the engine speed matches or exceeds the motorspeed.

According to other aspects of the method, the first clutch may be ahybrid one way clutch having rockers that are selectively shifted toconnect the engine to the electric motor. The first clutch may be ahydraulically actuated disconnect clutch. The method may furthercomprise applying the maximum pressure to the first clutch.

The above aspects of the disclosure and other aspects will be betterunderstood in view of the attached drawings and the following detaileddescription of the illustrated embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic representation of a modular hybrid transmissionwith a one way clutch connected in parallel with a disconnect clutch;

FIG. 2 is a graph of an engine start control showing engine and motorspeed and engine and motor torque through seven modes of operation; and

FIG. 3 is a diagrammatic representation of an alternative embodiment ofa modular hybrid transmission with a one way clutch or a hybrid rockerone way clutch connected in parallel with an oppositely oriented hybridrocker one way clutch.

DETAILED DESCRIPTION

The illustrated embodiments are disclosed with reference to thedrawings. However, it is to be understood that the disclosed embodimentsare intended to be merely examples that may be embodied in various andalternative forms. The figures are not necessarily to scale and somefeatures may be exaggerated or minimized to show details of particularcomponents. The specific structural and functional details disclosed arenot to be interpreted as limiting, but as a representative basis forteaching one skilled in the art how to practice the disclosed concepts.

Referring to FIG. 1, a modular hybrid transmission (MHT) system 10 isdiagrammatically illustrated and includes an electric fraction motor 12,a combustion engine 14, and a transmission gear box 16. A disconnectclutch 20 is operatively disposed between the engine 14 and the motor 12to selectively connect and disconnect the engine 14 from the motor 12. Adamper 22 may also be provided between the disconnect clutch 20 and theengine 14. A one way clutch (OWC) 24 is connected in parallel with thedisconnect clutch 20 between the damper 22 and the electric motor 12.

A starter motor 26 may be provided for starting the engine 14 in theembodiment shown in FIG. 1. It should be understood that other starterarrangements may be provided that may benefit from the conceptsdisclosed.

A launch clutch 28 is provided between the motor 12 and the transmissiongearbox 16. The launch clutch 28 provides torque to the transmissiongear box 16 from either or both of the motor 12 or engine 14. In theembodiment of FIG. 1, no torque converter is included in the gearbox. Atorque converter could be included in the combination and used in placeof the launch clutch 28.

Referring to FIG. 2, a graph of engine and motor torque and engine andmotor speed during engine start and engine shut down is provided for atransmission system 10 made in accordance with one embodiment of thisdisclosure. In mode 1, the motor 12 is providing torque for traction andthe engine 14 is not in operation. The vehicle in mode 1 is preparing tostart the engine 14 that is indicated by the line 30 that shows theengine speed increasing. The oscillating line 32 overlaid on line 30indicates that the rate of increase varies. The speed of the motor isillustrated by line 34 and is generally unchanged except that the motorspeed may increase a small amount during engine start because of theneed to maintain fluid pressure in the system or to allow a downstreamclutch to slip and provide torsional isolation relative to thedriveline.

Torque from the motor 12 is illustrated by line 36 that shows positivetorque is provided by the motor 12 through the first mode. Engine torqueillustrated by line 38 in mode 1 is at zero. As the engine speed 30increases speed, and enters mode 2 a small amount of torque is producedby the engine 14. In mode 3, the engine speed continues to increase andapproaches the same speed as the motor 12 as shown on line 34. When theengine speed matches the motor speed, mode 3 begins in which torquetransfer from the engine 14 begins while torque from the motor 12 isreduced. As used in this disclosure, the term “matches” should beunderstood to mean that the speed of rotation of the engine 14 is within5 rpm compared to the motor 12. In mode 3, the engine speed 30 is shownto match the motor speed 34 and motor torque 36 is reduced while theengine torque 38 increases.

Line 40 illustrates operation of the disconnect clutch 20. In mode 4 thedisconnect clutch 20 is beginning to be applied. However, it should beunderstood that the disconnect clutch 20 could be applied earlier inmode 3. The disconnect clutch 20 is applied to lock-up the motor 12 andengine 14. The engine 14 in mode 4 provides positive torque to drive thevehicle and also produces torque that is used to charge the battery (notshown).

In mode 4 with the vehicle being powered by the combustion engine 14pressure applied to the disconnect clutch 20 is shown by line 40 to beinitially at a normal operational level. The pressure command is reducedto zero when the disconnect clutch is released to disconnect the engine14 from the motor 12. In mode 5, the vehicle is preparing to transferfrom the engine 14 as a source of torque to the motor 12 as a source oftorque. In mode 6, the engine speed and motor speed are matched towithin 5 rpm. Motor torque 36 and engine torque 38 remain relativelyconstant through modes 4 and 5. However, during mode 6 the source oftorque is transferred from the engine 14 to the motor 12. At the end ofmode 6, the engine speed begins to be reduced until the engine 14 stops.

Referring to FIG. 3, an alternative embodiment having two variations isshown. The alternative embodiment of the modular hybrid transmission(MHT) system 40 includes an electric traction motor 42, a combustionengine 44, and a transmission gear box 46. A hybrid rocker one wayclutch 50 is operatively connected between the engine 44 and the motor42 that is adapted to connect and disconnect the engine 44 from themotor 42. The hybrid rocker one way clutch 50 is bi-directionallyrotatable and is lockable in one rotational direction by shifting therocker, as is known in the art. A damper 52 may also be provided betweenthe hybrid rocker one way clutch 50 and the engine 44.

In one variation, a one way clutch (OWC) 54 is connected in parallelwith the hybrid rocker one way clutch 50. Alternatively, a second hybridrocker one way clutch could be incorporated in place of the OWC 54. Oneadvantage of using a hybrid rocker one way clutch 50 instead of the OWC54 is that there is less parasitic power loss than with a frictionclutch type of OWC and can improve fuel economy. The hybrid rocker oneway clutch 54 includes a coil (not shown) that requires energy to shiftthe rocker and may be more expensive than a conventional OWC. Howeverthe hybrid rocker one way clutch 54 is expected to improve performancein terms of improved noise vibration and harshness. The hybrid rockerone way clutches 50 and 54 do not require additional hydraulic controland do not include friction clutch elements.

A starter motor 58 may be provided for starting the engine 44 in theembodiment shown in FIG. 4. It should be understood that other starterarrangements may be provided that may benefit from the conceptsdisclosed.

A launch clutch 60 is provided between the motor 42 and the transmissiongearbox 46. The launch clutch 60 provides torque to the transmissiongear box 46 from either or both of the motor 42 or engine 44. In theembodiment of FIG. 3, no torque converter is included in the gearbox. Atorque converter could be included in the combination and used in placeof the launch clutch 60.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms of the disclosed apparatusand method. Rather, the words used in the specification are words ofdescription rather than limitation, and it is understood that variouschanges may be made without departing from the spirit and scope of thedisclosure as claimed. The features of various implementing embodimentsmay be combined to form further embodiments of the disclosed concepts.

1. A transmission system having a combustion engine, an electric motorand a transmission, the system comprising: a clutch operativelyconnected between the engine and the motor; and a one way clutchconnected in parallel with the clutch that permits the engine toincrease speed with the clutch disengaged until the engine speed matchesa motor speed, wherein the engine provides positive torque through theone way clutch to the motor and transmission upon matching the motorspeed.
 2. The transmission system of claim 1 wherein the clutch is a wetclutch that is shifted by hydraulic pressure from a hydraulic pump. 3.The transmission system of claim 1 wherein upon the engine speed matchesthe motor speed, the one way clutch limits a speed of rotation of theengine to a speed of rotation of the motor by over running the one wayclutch in the event the speed of rotation of the engine exceeds thespeed of rotation of the motor.
 4. The transmission system of claim 1wherein the one way clutch is a hybrid one way clutch that has rockersthat may be shifted to engage the clutch in one rotational direction. 5.The transmission system of claim 4 wherein the clutch is a second hybridone way clutch that has rockers that may be shifted to engage the clutchin one rotational direction.
 6. The transmission system of claim 1wherein the clutch is a hybrid one way clutch that has rockers that maybe shifted to engage the clutch in one rotational direction.
 7. Atransmission system for a vehicle that has a combustion engine, anelectric motor and a transmission connected in series, the transmissionsystem comprising: a one way clutch that slips in a first rotationaldrive direction; and a hybrid one way clutch having selectively shiftedrockers is connected in parallel to the one way clutch between theengine and the motor, the rockers are actuated when an engine speedmatches a motor speed to shift the rockers from a bidirectional slipcondition to a one way slip condition locked in the first rotationaldrive direction.
 8. The transmission system of claim 7 wherein therockers when actuated causes the hybrid one way clutch to slip in asecond rotational drive direction.
 9. The transmission system of claim 7wherein when the engine speed matches the motor speed the one way clutchconnects the engine to the transmission to transmit torque to adriveline of the vehicle.
 10. The transmission system of claim 7 whereinthe one way clutch is a second hybrid one way clutch that locks prior towhen the engine speed matches the motor speed.
 11. A method of operatinga transmission system for a vehicle that has a combustion engine, anelectric motor and a transmission connected in series, a first clutchoperatively connected between the engine and the motor, and a one wayclutch connected in parallel with the first clutch, the methodcomprising: initiating an engine start operation; disengaging the firstclutch to disconnect the engine from the electric motor; and engagingthe one way clutch when an engine speed matches a motor speed.
 12. Themethod of claim 11 wherein the first clutch is a hybrid one way clutchhaving rockers that are selectively shifted to connect the engine to theelectric motor.
 13. The method of claim 11 wherein the first clutch is ahydraulically actuated disconnect clutch.
 14. The method of claim 11wherein the first clutch is a hybrid one way clutch with electricallyshifted rockers.
 15. The method of claim 14 wherein the one way clutchis a second hybrid one way clutch with electrically shifted rockers. 16.The method of claim 11 wherein the one way clutch is a hybrid one wayclutch with electrically shifted rockers.